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Antennas for MeerKAT

Antennas for MeerKAT. 13-14 March 2008. MeerKAT Semantics. K.A.T. = Karoo Array Telescope KAT is Afrikaans for cat MeerKAT: Afrikaans for “more cats”, also a small furry animal (from the mongoose family). MeerKAT Antenna Team. Antenna Pedestal & reflector Subcontracted to industry

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Antennas for MeerKAT

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  1. Antennas for MeerKAT 13-14 March 2008

  2. MeerKAT Semantics • K.A.T. = Karoo Array Telescope • KAT is Afrikaans for cat • MeerKAT: Afrikaans for “more cats”, also a small furry animal (from the mongoose family)

  3. MeerKAT Antenna Team • Antenna • Pedestal & reflector • Subcontracted to industry • Managed by Willem Esterhuyse • Feeds • Subcontracted to industry (EMSS Antennas) • Managed by LJ du Toit • Close interaction with RF & Reflector • RF • Subcontracted to industry • Managed by Venkat Lakshmanan

  4. MeerKAT Intention • South African funds (~ $100 x 106) • Funded by Dept. of Science & Technology • Administered by National Research Foundation • To be built irrespective of SKA site allocation • Must be respectable instrument, not just good • Must be of relevance to SKA • N ~ 80 • D ~ 12m • Full instrument first light Q4, 2012

  5. MeerKAT & KAT-7 Site • Carnavon, Northern Cape, South Africa

  6. MeerKAT & KAT-7 Site

  7. MeerKAT Phased Implementation • XDM: Q4, 2005 to Q4, 2007 • Almost a done deal • KAT-7: Q1, 2008 to Q4, 2009 • This year and next • MeerKAT: Q1, 2008 to Q4, 2012 • This year, up to 2012

  8. XDM: Q4, 2005 to Q4, 2007 • Single dish prototype at Hartebeesthoek, outside Pretoria • Composite surface, concrete pedestal, metal support structure • Antenna structure & surface R&D, manufacturing by IST Dynamics • Diameter 15m, F = 7.5m (F/D = 0.5) • El over Az, feed rotator (1.5m diameter disk) • Prime-focus fed (four large metal struts) • Frequency band: 1414 to 1670 MHz • Stepped-horn & stepped-ridge OMT (EMSS), un-cooled • Feed cluster: Seven non-overlapping beams (two populated) • Two linear polarizations, analogue RF over fiber (COTS) • Thermally stabilized COTS LNAs • Prototyping test-bed, not a science instrument • Used to set up synergy amongst engineering team • System Engineering busy evaluating performance

  9. KAT-7: Q1, 2008 to Q4, 2009 • Seven antenna interferometer, on proposed SKA site • First-light scheduled to be Q3, 2009 • Limited science instrument, and interferometer test-bed • Although small, must be respectable instrument, prototyping errors to be avoided first time around • Composite surface, concrete pedestal, metal support structure • Antenna structure & surface: Tenders to go out within weeks • Diameter 12m, F = 4.56m (F/D = 0.38, optimized for horn & WBF at prime focus • El over Az, single-pixel feed, no field rotator • Frequency band: 1200 to 2000 MHz (dish tolerances allow >2GHz) • Wide flare-angle corrugated horn (four metal struts) • Cryogenically cooled OMT & Receiver (probably Sterling) • Two linear polarizations, analogue RF over fiber (COTS) • Will allow evaluation of remote instrument logistics

  10. MeerKAT: Q1, 2008 to Q4, 2012 • N ~ 80 interferometer on proposed SKA site • Probable topology: Similar to KAT-7 • Unless dynamic range requirements dictate otherwise • Unless wide-band feed require different F/D • Unless upper frequency too high • Dynamic Range Considerations • N > 80 to be considered • Main beam stability, sidelobe and polarization requirements? • Offset? • Offset and folded? • Feed rotator required? • Tightened mechanical tolerances?

  11. KAT-7: Surface Tolerance

  12. KAT-7: Status • F/D Study • Time scales (dish construction ahead) • Accommodate MeerKAT (XDM was for FPAs) • No finished feed available • Ying wide flare horn • Parallel dipoles(radiating as log-periodic antennas) • Determine range of possiblebeam widths

  13. KAT-7: Status • F/D Study • Look at different system temperatures • Optimise Ae / Tsys • F/D = 0.38

  14. KAT-7: Status • Horn • Classic corrugated horn • Wide flare (prime focus) • Size → sub-reflector • J(x)/x distribution • Optimised on-dish • Gain • Spill over • Still varying radius

  15. KAT-7: Status • Horn • Pattern almost 1 to 2 GHz • Match 1.2 to 2 GHz (without OMT)

  16. KAT-7: Status

  17. KAT-7: Status • Other engineering work for 2008… • OMT development • Cryo-cooling • He versus LN2 choice • Development • Cryostat development • Cool-box development • Calibration Signal Injection • LNA choice

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